It is well known that carboxylation may be used to increase latex colloidal stability, provide functional sites for further reaction, and increase adhesion properties and surface characteristics Providing functional sites for further reaction is particularly important to fibrous materials binding and paper saturation. The increase in adhesion properties and surface characteristics is important for coating applications.
The degree of carboxylation is measured by acid number. Acid number is defined as the number of milligrams of potassium hydroxide required to neutralize the free acid in the polymer. Generally, increasing the degree of carboxylation increases the viscosity of a latex. This increase of viscosity due to increase of carboxylation is further amplified at higher pH values and at higher total solid levels. These higher pH values and higher total solids become critical in various applications such as in fibrous materials binding, paper saturation, and coating applications.
European Patent No. 1,412,907 to Tajima assigned to Sumitomo Naugatuck Co., LTD discloses copolymer latex and paper coating compositions thereof. This patent discloses conjugated diolefin copolymer latexes, preferably butadiene latexes, combined with an alkyl ester of an unsaturated carboxylic acid, and a hydroxy alkyl-containing unsaturated monomer, an unsaturated carboxylic acid monomer, and an alkenyl aromatic monomer.
It is an important aspect of this invention to provide a latex that contains an acid mixture with at least one acid being methylenesuccinic acid.